1. Field of the Description
This description is generally directed toward methods of interlacing images for use in printing images viewable through a lenticular lens array or lens sheet, and, more particularly, to methods of interlacing to provide an increased amount of information (e.g., interlaced images or frames) underneath each lenticule to facilitate use of thinner lens sheets.
2. Relevant Background
Elaborate graphics or visual displays can be produced through the use of sheets of lenticular lens arrays as these arrays of lenses can be combined with printed interlaced images to provide three-dimensional (3D) and animated imagery. For example, lenticular lens material is used in the packaging industry for creating promotional material with appealing graphics and typically involves producing a sheet of lenticular lens material and adhesively attaching the lenticular lens material to a separately produced object for display. The production of lenticular lenses is well known and described in detail in a number of U.S. patents, including U.S. Pat. No. 5,967,032 to Bravenec et al. and U.S. Pat. No. 6,781,761 to Raymond.
In general, the production process includes selecting segments from visual images to create a desired visual effect, slicing each segment into a predefined number of slices or elements (such as 10 to 30 or more slices per segment), and interlacing the segments and their slices (i.e., planning the layout of the numerous images). Lenticular lenses or lens sheets are then fabricated according to the number of slices or the interlacing may be performed to suit the lens sheets, e.g., to suit a particular lenticules or lenses per inch (LPI) of the lens sheet. The lenticular lenses generally include a transparent web that has a flat side or layer and a side with optical ridges and grooves formed by linear or elongated lenticules (i.e., lenses) arranged side-by-side with the lenticules or optical ridges extending parallel to each other over the length of the transparent web. To provide the unique visual effects, ink (e.g., four color ink) is applied to or printed directly on the flat side of the transparent web to form a thin ink layer (or a printed image is applied with adhesive to the back or planar side of the transparent web), which is then viewable through the transparent web of optical ridges.
Each lenticule or lens of the lenticular layer is paired or mapped to a set or number of the interlaced image slices or elements. Generally, only one of the slices is visible through the lenticule at a time based on the position of the lenticule relative to a viewer's eye. In other words, the animation, 3D, or other graphic effect is achieved by moving the lenticule or the viewer's position to sequentially view each of the interlaced image slices under the lenticule and allow a viewer to see each segment of the image by combining the slices viewed from all the lenticules.
In producing conventional lenticular lens material, it is desirable to use as little material as possible, i.e., to produce effective lenticules or lenticular lens arrays with as thin web material as possible. Decreasing lens thickness is also desirable to facilitate fabrication using techniques such as web printing that are very difficult or impractical with thicker lens materials. Thin lenticular lens material is desired to save on material costs and to provide a relatively flexible lens material or substrate that can be easily applied to products and product containers, such as in a label that can be attached to a box or to a bottle as part of a wraparound label or on a cup to provide desirable visual effects. To make lenticular lens materials thinner, the whole structure must be properly scaled downward together. In other words, the lenticules and the printed interlaced image must be shrunk or made smaller together to allow proper mapping of the image slices to the lenticules.
However, such shrinking of the lenticules has proven very difficult with limitations associated with printing the interlaced images often preventing the lens layer or web from being made very thin. As noted above, all the interlaced slices for each segment are placed underneath a single lenticule such that numerous slices have to be printed with very little width to be mapped to the lenticules width or pitch. With coarser lens arrays (i.e., with lower frequency or LPI), the printing can be accomplished more easily and mapping to lenticules of the image slices achieved more accurately. However, coarser lens arrays with frequencies of 10 to 30 LPI tend to be very thick because general physics or optical rules for focusing with conventional lenticular material require that more lens thickness or more lens material be provided to achieve effective focusing. For example, a 15 LPI lenticular lens array with a fairly common viewing angle (such as a 22-degree viewing angle) may be mapped to an interlaced image that printed or provided directly behind the lenticular lens array, with each of the lenticules in the lens array being mapped to or paired with all image slices of a paired segment of the interlaced image. If the lens array is formed from acrylic, the lens array would need to be about ⅜-inch thick to enable the lenticules to properly focus on the paired image slices.
Traditionally, lenticular printing has been a multi-step process that includes creating a lenticular image from at least two images and combining it with a lenticular lens. The lenticular printing process can be used to create various frames of animation for a motion effect, can be used for offsetting the various layers at different increments for a 3D effect, or can be used simply to show a set of alternate images that may appear to transform into each other. Once the various images are collected, they are flattened into individual, different frame files, and, then, the frame files are digitally combined into a single final file for use in printing an interlaced image. The digital combining process is often called “interlacing.”
Once the combined or interlaced file is generated, it can be used to print an interlaced image directly to the back (or smooth/planar) side of the lenticular lens sheet. In other applications, the interlaced image may be printed onto a substrate (e.g., a synthetic paper or the like), which is then laminated onto the lens (e.g., a transparent adhesive may be used to attach the substrate with the printed interlaced image onto the lenticular lens sheet). When printing to the backside of the lens sheet, the registration of the thin slices or elongated interlaced images to the lenses is important during the lithographic or screen printing process to avoid or at least limit ghosting or other effects that produce poor imagery.
With traditional lenticular interlacing, each image is arranged or sliced into strips, which are then interlaced with one or more similarly arranged or sliced images such as by splicing or interlacing. The end result is that a person's single eye looking at the printed interlaced image through the lenticular lens array (or lens sheet) sees a single whole image while a person's two eyes may see different images (e.g., right and left-eye images), which provides a desired autostereoscopic or 3D perception.
The process of creating strips of information from graphics or images and then scrambling them into a single image for printing underneath a lens sheet can be problematic. One significant problem is that there is a limitation on the amount of information (e.g., pixels) that can be placed underneath each lenticule or elongated lens in the lens sheet. For example, a lens or lenticule has a particular size (e.g., a width set by the LPI of the lens sheet or lens array), and the printer used to provide the printed interlaced image may have a particular resolution (e.g., dots per inch (DPI)). Hence, these limitations or parameters of a lenticular product or assembly (e.g., a security stamp or security thread for a bank note or piece of currency) define the maximum number of frames or images that can be interlaced and then printed on a lens sheet by the equation: Maximum number of frames=DPI/LPI.
FIG. 1 illustrates a cross-sectional view (or end view) of a very simple lenticular device or assembly 100 that is useful for discussing these limitations associated with traditional lenticular printing and interlacing. As shown, the assembly 100 includes a single lenticule or elongated lens 110 with a planar side or base 112 of a particular width, LW (lenticule size as defined by the LPI of a sheet including lens/lenticule 110). An ink layer or printed interlaced image 120 is provided directly onto the back side or base 112 of the lenticule 110, and, in this example, the interlaced image 120 includes five image slices 124 (e.g., long, thin portions of five different images/frames) that would extend the length of the lenticule 110 in a parallel manner (parallel to each other and to the longitudinal axis of the lenticule/lens 110).
In the assembly or device 100, the lens size, LW, and pixel size is such that the lens 110 can only work well with a maximum of five interlaces or image slices 124 (e.g., five pixels with each pixel being associated with one of the five interlaced frames/images). These are shown to be exactly aligned with the lens 110 but may, in practice, be somewhat offset while still being parallel to the longitudinal axis of the lens 110 and still achieve a desirable image when viewed through the lens 110. The interlacing is orthogonal in that the five pixels extend orthogonally across the lens 110 relative to its longitudinal axes (e.g., the elongated slices of the image extend parallel to the longitudinal axis of the lens 110 such that side-by-side pixels associated with these slices/interlaces extend across the lens width, LW).
However, in order to achieve a 3D effect with lenticular sheets, the minimum number of frames needed is six or more images/frames. This means, for example, that for a 1200 DPI output device (e.g., printer) the lenticular lenses must have a width associated with a 200 LPI or higher (where LPI=DPI/Number of frames or, in this case, 200 LPI=1200 DPI/6 frames). This relationship between resolution of the output device, the number of frames needed to produce 3D, and the lens size creates a significant restriction to developing thinner lenticules and corresponding thinner lenticular products (such as security threads or stamps for currency or bank notes). However, it should be understood that the limitation is not the ability to fabricate thinner lens sheets because lens sheets that are very thin can readily be produced with presently available technology. Instead, the restriction or challenge to providing thin lens sheets comes from the high resolution that would be required, and, therefore, the limitation of the number of frames that can be printed on or underneath smaller sized lenses (e.g., lenses with smaller widths or LW).
FIG. 2 illustrates a top perspective view of a lenticular product or assembly 200 that may use conventional or traditional interlacing. As shown, the assembly 200 includes a lens sheet or lens array 210 that may be formed of a thickness of plastic or other transparent material. On a top or exposed side, the lens sheet 210 is grooved or shaped to provide a number of lenticules or elongated lenses 214 that extend in a parallel manner from one end to the other of the sheet 210. As is common, the lenticules 214 extend “vertically” in the array or sheet 210 or with their longitudinal axes being orthogonal to the top and bottom edges 211, 213 of the sheet 210 (or being parallel to left and right side edges). Each lenticule or lens 214 has a size or width, LW, that is defined by the LPI of the lens sheet 210.
In the lenticular assembly 200, an ink layer 220 is printed directly upon a planar back side or bottom side 216 of the lens sheet 210 (or may be provided on a substrate that is laminated onto the lens sheet 210). The ink layer 220 is printed to provide a number of interlaced images or slices 224 underneath each lenticule 214 such as to provide a 3D effect. As shown, the interlaced image of ink layer 220 has five slices 224 associated with five different frames underneath each lenticule 214, with different slices of the same frame being provided under different lenticules 214 in the sheet 210. In this case, the image file for printed ink layer 220 was created with five pixels to match the size, LW, of each lens 214.
Lenticular devices may also use lenses or lenticules that are provided in a sheet or array with an angular arrangement, e.g., not parallel or orthogonal to edges of the sheet/array. FIG. 3 illustrates a conventional slant lens lenticular device or assembly 300 in which a lens or lenticular sheet 310 is combined with an interlaced image provided in an ink layer 320. The lens sheet 310 includes a number of lenticules or lenses 314 on a top or exposed side, and the lenticules 314 extend parallel to each other but, in this lens sheet 310, the lenticules 314 are not arranged vertically or horizontally. In other words, the lenticules or lenses 314 are “slanted” with their longitudinal axes, AxisLong, as shown at 315 arranged to each be at a particular angle, θ, relative to a side edge 311 of the lens sheet 310, with the slant angle, θ, being less than 90 degrees (not orthogonal) such as 20 to 60 degrees or the like. Again, each lens 310 has a size or width, LW, set by the LPI of the sheet 310 that may limit the number of image slices that may be placed underneath each of the lenses 314 with conventional interlacing techniques.
The lenticular assembly 300 further includes an ink layer 320 providing a printed interlaced image with a number (here five) of slices 324 provided under each lens 314. In other words, instead of having the interlaces or slices 324 provided with “vertical” strips that are spliced together, the ink layer 320 provides the image with slanted strips 324 matching the slant angle, θ, of the lenses 314. Hence, the interlacing for slant lens sheets such as sheet 310 has traditionally involved arranging the elongated slices of a number of images to extend parallel to each other and also to the longitudinal axis, AxisLong, as shown at 315 of the lenses 314. Hence, the interlacing of the device 300 again is to match the size of the lenses 314 with five pixels arranged orthogonally to the longitudinal axis, AxisLong (e.g., to extend across the width, LW, of the lens 314). As can be seen, the use of slant lens does not increase the amount of information provided under the lens array when traditional interlacing is used to generate the interlaced image.
There remains a need for methods for providing an interlaced image (i.e., interlacing methods) that allow additional information to be provided under the lenses or lenticules of a sheet of lenticular material (or a lens sheet). Preferably, such interlacing methods would be useful with existing and to-be-built output devices (e.g., printers) to allow lenticular products to be provided with desirable imagery (e.g., 3D imagery) with much lower thicknesses of lenticular material or lens sheets, e.g., to support use of lenticular assemblies or elements as security threads, stamps, and the like in bank notes, currency, and other items.